Various optical displacement encoders are known that use a readhead having an optical arrangement that images a scale pattern to a photodetector arrangement in the readhead. The image of the scale pattern displaces in tandem with the scale member, and the movement or position of the displaced scale pattern image is detected with a photodetector arrangement. Conventional imaging, self-imaging (also called Talbot imaging), and/or shadow imaging may be used to provide the scale pattern image in various configurations.
One type of configuration that is utilized in some optical encoders is a telecentric arrangement. U.S. Pat. Nos. 7,186,969; 7,307,789; and 7,435,945, each of which is hereby incorporated herein by reference in its entirety, disclose various encoder configurations that utilize either singly or doubly telecentric imaging systems for imaging the periodic pattern of light and sensing displacement of the periodic scale structure. Telecentric imaging systems provide certain desirable features in such optical encoders.
One issue with regard to the design of such optical encoders is that users generally prefer that the readheads and scales of the encoders be as compact as possible. A compact encoder is more convenient to install in a variety of applications. For certain precision measurement applications, high resolution is also required. However, various known encoders fail to provide certain combinations of high resolution, range-to-resolution ratio, robustness, large field of view, and design features which allow a number of encoder resolutions to be provided using shared manufacturing techniques and components, and which facilitate low cost as desired by users of encoders. Improved configurations of encoders that provide such combinations would be desirable.